The present invention relates to a sheet reversing apparatus which can positively register sheets being fed and feed the sheets one by one. The sheet reversing apparatus is applicable to a laser beam printer for performing the recording or printing on both surfaces of the sheet, but is not limited to such application.
In printing machines such as a laser beam printer and the like, when the both-surface recording is effected, first of all, a first surface of a sheet is printed. Then, the sheet is fed, with the printed first surface turned over by a sheet reversing apparatus, from the sheet reversing apparatus to a printing station again, and a second surface of the sheet is printed at the printing station.
Conventional reversing apparatuses were divided into generally two types, in one of which the incoming sheet was continuously fed out as it was, and in the other of which a plurality of sheets were once stacked and thereafter the sheet was separated and fed one by one from the bottom of the sheet stack. Accordingly, in the past, there was no sheet reversing apparatus wherein the receipt of a next sheet and the feeding-out the previously received sheet were simultaneously and continuously effected while a plurality of sheets were stacked.
In the conventional reversing apparatus of the former type, for example, a continuously rotating rubber impeller is used as a sheet hold-down means, and a regulating means such as a stopper is also provided to cooperate with the hold-down means. The sheet is registered by these means and is continuously received by the reversing apparatus to be fed out as it is.
In the conventional reversing apparatus of the latter type, a stopper means is movably arranged in the vicinity of the stacking station, which stopper means serves to register and stack the sheets during the stacking operation. On the other hand, during the sheet separating and feeding operation, the stopper means is separated from the sheet stack to release the urging force of the stopper means acting on the sheet stack, thereby preventing the double-feeding of the sheets. Further, as disclosed in the U.S. Pat. No. 4,275,877, in a sheet reversing apparatus wherein the sheet separating and feeding operation is effected by using a vacuum suction, the whole stacking station is inclined downwardly with respect to a horizontal plane, and a rear guide is provided at the stacking station. In addition, an air blowing portion is arranged in confronting relation to the stacking station, and a feeding portion is disposed below the stacking station. Sheets fed to the stacking station are abutted against the rear guide to be registered and are successively stacked. Thereafter, by intermittently activating the air blowing portion and the feeding portion, an lowermost sheet in the sheet stack is attracted by the vacuum suction force, whereas the remaining sheets are floated to separate from the lowermost sheet, thereby preventing the multifeeds of the sheets.
However, the arrangement in the reversing apparatus of the former type arose a problem when it was used with a high speed printer. That is to say, in the high speed printer, it is necessary to previously convert the printing information into dots and store them in a memory. Thus, in order to continuously reverse the sheets, the memory means therefor becomes large-sized as that used in a large-sized computer, which leads in the increase in the cost of the whole printer.
On the other hand, in the conventional reversing apparatus of the latter type in which the sheets are separated and fed after they have previously been stacked, it is difficult to control the air system for separating the sheet from the bottom of the sheet stack and attracting the sheet intermittently at a high speed. Consequently, there arose a problem that it was impossible to reverse and feed the sheet at a high speed.